Phosphor and plasma display unit

ABSTRACT

Disclosed here is a plasma display unit that employs phosphors having an amount of charge controlled close to zero, by which degradation in luminance, color temperature, and charge characteristics can be minimized. A phosphor bearing positive or negative charge is coated with a compound for controlling the amount of charge of the phosphor through a strong chemical bonding, whereby the amount of charge of a phosphor can be suppressed within ±0.01 μC/g. Controlling the amount of charge of phosphors close to zero can keep impurity gases away from the phosphor particle when the panel is in operation, suppressing problems critical to driving a plasma display unit, such as luminance degradation of phosphors, improper alignment of color in panel operation, luminance degradation when the panel displays all white.

TECHNICAL FIELD

The present invention relates to a plasma display unit employingphosphors that emit light by ultraviolet excitation, and the plasmadisplay unit is typically used for the screen of a TV

BACKGROUND ART

In color display devices employed for image display on computers or TVs,a plasma display unit having a plasma display panel (hereinafterreferred to as a PDP) has recently received considerable attention as acolor display device with large sized screen but lightweight body due toits low-profile structure.

A PDP displays image in full color by performing an additive colorprocess on red, green, and blue—known as the three primary colors. Torealize the full color display, a PDP has phosphor layers that arerespectively prepared for emitting red (R), green (G), and blue (B) ofthe three primary colors. A phosphor layer is formed of phosphorparticles. The phosphor particles are excited by ultraviolet raysgenerated in discharge cells in the PDP, so that visible lights of red,green, and blue are produced.

As the chemical compounds typically used for the phosphors above are,for example, Zn₂SiO₄:Mn²⁺, which is a green emitter with a tendency tobe negatively (−) charged; BaMgAl₁₀O₁₇:Eu²⁺, which is a blue emitterwith a tendency to be positively (+) charged; and (Y,Gd) BO₃:Eu³⁺,Y₂O₃:Eu³⁺, which are red emitters with a tendency to be positively (+)charged (for example, see O plus E, No. 195, pp. 99-100, Feb. 1996).

Each phosphor is manufactured through solid phase reaction—after mixedpredetermined material, the mixture is baked at high temperature beyond1000° C. (for example, see Phosphor Handbook, pp. 219-225, Ohm-sha).Because the baking process sinters the phosphor particles, the phosphorparticles are crushed to eliminate clotted particles, but are crushedlightly so as not to break the crystallized structure that invites poorluminance. After crushing, the phosphor particles are classified toobtain an average particle diameter for each phosphor particle:preferably, 2-5 μm for the red, and the green phosphors, 3-10 μm for theblue phosphor. The reason why the phosphor particles should be lightlycrushed and classified is described below. To form a phosphor layer of aPDP, manufacturers have conventionally employed a screen printing methodin which the phosphor particles of each color are processed into pasteand the paste is applied by screen printing; and an inkjet applyingmethod in which paste-like phosphor particles are applied with a nozzle(that is introduced in, for example, Japanese Patent UnexaminedPublication No. H06-273425). The light crushing and classification caneliminate clotted particles that can cause an uneven application of thephosphor paste or a clogged nozzle in the phosphor paste applyingprocess.

That is, the classified phosphor particles after experienced lightcrushing offer a uniform particle diameter and particle sizedistribution, whereby a smooth surface without irregularities can beexpected. In forming a phosphor layer, the phosphor particles havingsmaller, closer to uniformity in size of a particle diameter and closerto a sphere in shape can offer a smoother coating surface. Suchdesirable particles improve filling density in a phosphor layer;accordingly, increasing luminance efficiency by virtue of increase inemitting surface area of phosphor particles. The advantages abovecontribute to stable operations in driving a PDP.

On the other hand, a phosphor is an insulant, which is basically formedof a crystal that is stoichiometrically produced from various kinds ofelements. The chemical bond of the crystal itself is the ionic bondrather than the covalent bond. A phosphor exhibits different chargecharacteristics according to electronegativity and the crystal structureof the elements forming the phosphor. Some suggestions about stabilizingthe charge characteristics of phosphors have disclosed (see, forexample, Japanese Patent Unexamined Publication No. H11-86735, JapanesePatent Unexamined Publication No. 2001-236893, and Japanese PatentUnexamined Publication No. 2002-93321).

A PDP employing the combination of conventional phosphor material hasproblems below, which are caused by the charge characteristics of eachphosphor particle.

Specifically, a PDP employing the conventional combination ofZn₂SiO₄:Mn²⁺ for green; BaMgAl₁₀O₁₇:Eu²⁺ for blue; and (Y,Gd) BO₃:Eu³⁺or Y₂O₃:Eu²⁺ for red has a pending problem below. Of the phosphorsemployed above, the surfaces of the blue and the red phosphor particlesbear positive (+) charge, having an amount of charge of ranging from+1.2 μC/g to +1.1 μC/g measured by a blow-off charge measuring method,which is a widely used method for measuring an amount of charge ofpowders). On the other hand, the surface of the green phosphor particleof Zn₂SiO₄:Mn²⁺ bears negative (−) charge, having an amount of charge of−1.5° C./g measured by the same method. The reason why the surface ofthe green phosphor particle bears negative charge results from the factbelow. Compared to the stoichiometric ratio of zinc oxide (ZnO) tosilicon oxide (SiO₂) of 2 to 1, the green phosphor of Zn₂SiO₄:Mn²⁺ inthe practical use contains the amount of SiO₂ has greater than thestoichiometrically determined amount, having a mixture ratio ZnO to SiO₂of 1.5 to 1. The crystal of Zn₂SiO₄:Mn²⁺ contains excessive SiO₂ on thesurface, and SiO₂ is likely to bear negative (−) charge due to a greatelectronegativity on its physical properties.

Generally, in a PDP having a phosphor layer in which a negatively (−)charged phosphor and a positively (+) charged phosphor coexist, thedifference in the charge characteristics introduces variations in theamount of discharge through the repeated PDP driving operations. Due tothe variations in the charge characteristics, a PDP can't keep aconsistent voltage of address discharge on the application of voltagefor display, resulting in discharge failure, such as variations indischarge and no discharge.

The difference in charge characteristics has also a problem in formingthe phosphor layer using an inkjet applying method. In the inkjetmethod, phosphor ink is continuously fed through a narrow nozzle to abarrier rib on the rear substrate. The phosphor ink, which is positively(+) or negatively (−) charged due to the friction caused at ink-jetting,is often launched with a bend, and therefore, the ink cannot be evenlyapplied on the surface of the barrier ribs. In particular, employingeach of the three phosphor ink having difference in chargecharacteristics makes charge control of the rear substrate difficult,thereby inviting the uneven application of the phosphor ink that spoilsthe view on the PDP.

In driving a PDP, a 147 nm-ultraviolet ray, which is a resonance linewith respect to xenon (Xe), is employed for the excitation source ofemission. Because of such a short wavelength and therefore poorpermeability of the ultraviolet rays, the excitation occurs at only thesurface area of the phosphor. That is, the surface condition of thephosphor particles is the most susceptible to luminance degradation. Thephosphor surfaces bearing positive or negative charge tell that manydangling bonds occur on the surface of the phosphor particles. Such asurface condition easily captures impurity gases including ahydrocarbon-based gas generated in a PDP. The captured impurity gasesare decomposed by plasmatic activity in the PDP to create activehydrogen (proton), by which the surface of the phosphor is reduced tonon-crystalloid. This is the main factor that leads to luminancedegradation. Besides, in aging or driving a PDP, the phosphor surfacebearing charge encourages a collision between positive (+) ions, such asNe⁺, Xe⁺, H⁺, or between negative (−) ions, such as CH_(X) ^(n−)(hydrocarbon-based gas), O²⁻, in discharge plasma, thereby causingcrystal destruction. The phosphor surface bearing charge, as describedabove, can lead to a fatal degradation including luminance degradationof a PDP.

The present invention addresses the problems above. It is therefore theobject of the invention to control the amount of charge of the phosphorsso that the absolute value of the amount of charge of eachphosphor—green, blue, and red—is determined to be at most 0.01 μC/g,preferably, to be zero.

DISCLOSURE OF THE INVENTION

To achieve the aforementioned object, the plasma display panel (PDP) ofthe present invention has a structure at least formed of a front panelcontaining a plurality of display electrode pairs disposed on a glasssubstrate, and a rear panel containing a plurality of address electrodesand a phosphor layer for emitting by discharging. The front panel andthe rear panel are oppositely situated so as to form discharge spacetherebetween, and the display electrode pairs on the front panel and theaddress electrodes on the rear panel form discharge cells. According tosuch structured PDP of the invention, surface charge of the phosphor ofthe phosphor layer is determined to be ±0.01 μC/g or less.

Through the control of the surface charge, the phosphors have almost thesame amounts of charge (i.e., nearly zero), thereby providing aconsistent address discharge. Accordingly, the amount of charge on thesurface of each phosphor are substantially the same. Such an improvedsurface condition of the phosphor can minimize inconsistent dischargeand other discharge failures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view generally illustrating the structure of a PDP,with a front glass plate removed, of an exemplary embodiment of theinvention.

FIG. 2 is a partly sectioned perspective view indicative of the imagedisplay area of the PDP of the embodiment.

FIG. 3 is a block diagram of the whole structure of a plasma displayunit of the embodiment.

FIG. 4 is a partial sectional view illustrating the structure of theimage display area of the PDP of the embodiment.

FIG. 5 shows the general structure of an ink dispenser used for forminga phosphor layer in the embodiment.

DETAILED DESCRIPTION OF CARRYING OUT OF THE INVENTION

Hereinafter will be described in detail an exemplary embodiment of thepresent invention.

First, a plasma display unit of the embodiment of the present inventionis described with reference to accompanying drawings.

FIG. 1 is a schematic plan view of plasma display panel (PDP) 100, withfront glass substrate 101 removed. FIG. 2 is a partly sectionedperspective view showing image display area 123. In FIG. 1, displayelectrodes 103 forming the display electrode pairs, display scanelectrodes 104, and address electrodes 107 are partly omitted for thesake of clarity. Now will be described the structure of PDP 100 withreference to FIGS. 1 and 2.

In FIG. 1, PDP 100 contains front glass substrate 101 (not shown), rearglass substrate 102, N display electrodes 103, N display scan electrodes104 (where, a parenthesized N indicates the N^(th) electrode), M addresselectrode 107 (where, a parenthesized M indicates the M^(th) electrode),and hermetic seal layer 121 indicated by diagonal lines. The PDP has anelectrode matrix having a three-electrode structure made of respectiveelectrodes 103, 104, and 107. Discharge cells are formed at therespective intersections of display electrodes 103 and addresselectrodes 107. Display electrodes 103, display scan electrodes 104,dielectric glass layer 105, and MgO protective layer 106 are, as shownin FIG. 2, disposed on a principle surface of front glass substrate 101.On the other hand, disposed on a principle surface of rear glasssubstrate 102 are address electrodes 107, dielectric glass layer 108,barrier ribs 109, and phosphor layers 110R, 110G, 110B. The twosubstrates are sealed with each other so as to form discharge space 122therebetween. Discharge space 122 is filled with a discharge gas. ThePDP structured above is connected to an external driver circuit tocomplete a plasma display unit.

FIG. 3 is a block diagram showing the whole structure of plasma displayunit 160. Plasma display unit 160 is mainly formed of PDP 100, anddriver circuit 150 that contains display driver circuit 153, displayscan driver circuit 154, address driver circuit 155, controller 152. Indriving operations of plasma display unit 160, according to the controlof controller 152, a voltage is applied to each display scan electrode104 and each address electrode 107 of a cell to be lit for addressdischarge therebetween. Then, a pulse voltage is applied to displayelectrode 103 and display scan electrode 104 for sustain discharge. Thesustain discharge generates ultraviolet light in the cell. The phosphorlayers excited by the ultraviolet light emit light, thereby lighting thecell. In this way, combination of lit and unlit cells of the respectivecolors produces image on the display.

Now will be described a method of manufacturing PDP 100 with referenceto FIGS. 1 and 2.

The description is firstly given on the front panel. On front glasssubstrate 101, N display electrodes 103 and N display scan electrodes104 are arranged parallel to each other, like stripes. (In FIG. 2, onlytwo of respective electrodes are shown for simplicity.) Thereafter, theelectrodes are covered with dielectric glass layer 105, and further overwhich, MgO protective layer 106 is formed. Display electrodes 103 anddisplay scan electrodes 104 are made of silver. These electrodes areformed by applying silver paste for electrodes by screen printing andthen, the paste is baked. Dielectric glass layer 105 is formed byapplying a paste containing lead glass material by screen printing, andbaking the paste at a predetermined temperature for a predeterminedperiod of time (e.g. at 560° C. for 20 min.) to obtain a desiredthickness (approx. 20 μm). As for the paste containing lead glassmaterial, a mixture of 70 wt % of lead oxide (PbO), 15 wt % of boronoxide (B₂O₃), 10 wt % of silicon oxide ((SiO₂), 5 wt % of aluminum oxide(Al₂O₃) and an organic binder (α-terpineol containing 10% of ethylcellulose dissolved therein) is often used. The aforementioned organicbinder contains a resin dissolved in an organic solvent. Acrylic resincan be used as a resin other than the ethyl cellulose, andn-butylcarbitol as an organic solvent. Further, a dispersant—for,example, glyceryl trileate—can be mixed into such an organic binder. MgOprotective layer 106 is made of magnesium oxide (MgO). Protective layer106 is formed into a predetermined thickness (approx. 0.5 μm) bysputtering or chemical vapor deposition (CVD) method.

Now, the explanation turns to the rear panel. First, silver paste isapplied to rear glass substrate 102 by screen printing. And then, thepaste is baked to form M address electrodes 107 in lines. Next,dielectric glass layer 108 is formed by applying a paste containing leadglass material onto the address electrodes by screen printing. Barrierribs 109 are made of photosensitive paste containing lead glassmaterial. The paste is applied over the dielectric glass layer forpattern forming by photography method and then the paste is baked.Barrier ribs 109 are thus formed. Barrier ribs 109 divide, in thedirection of the lines, discharge space 122 into respective cells (i.e.,unit emission area).

FIG. 4 is a partially sectional view of PDP 100. As shown in FIG. 4,interval W between barrier ribs 109 is determined to a value rangingfrom approx. 130 to 240 μm so as to be suitable for a 32-50 in. highdefinition television (HD-TV). In each groove between barrier ribs 109,phosphor layers 110R for red, 110G for green, and 110B for blue areformed. The amount of charge of each phosphor is controlled ranging−0.01 μC/g to +0.01 μC/g. It is preferable that phosphor layers 110R,110G, 110B are formed so as to have thickness L in the direction oflayer being approx. 8 to 25 times the average diameter of phosphorparticles of each color. That is, in order to constantly achieve acertain luminance (emission efficiency) when a phosphor layer isirradiated with an amount of ultraviolet light, the phosphor layer needsto absorb ultraviolet light generated in the discharged space, notallowing the ultraviolet light to pass through the layers. For thispurpose, it is desirable that the phosphor layer has a thickness formedof at least eight layered-, preferable, approx. 20 layered-phosphorparticles. Having a thickness beyond 20-layered structure almost“saturates” emission efficiency—discharge space 122 cannot be kept asufficiently large space due to the thickened layer.

Here will be described how to form phosphor layers 110R, 110G, and 110B.FIG. 5 is a schematic diagram showing the structure of an ink dispenserused in forming phosphor layers 110R, 110G, and 110B. As shown in FIG.5, ink dispenser 200 contains server 210, pressure pump 220, and header230. Phosphor ink 250 is stored in server 210 and is fed, withapplication of pressure by pressure pump 220, to header 230. Header 230has ink chamber 230 a and nozzle 240. Phosphor ink 250, which was fed toink chamber 230 a with application of pressure, is continuously ejectedfrom nozzle 240. It is desirable that bore diameter D of nozzle 240 issized at least 30 μm to prevent clogging of the nozzle. It is alsodesirable that bore diameter D is equal to or smaller than interval Wbetween barrier ribs 109 (approx. 130 to 200 μm) to properly apply theink into the groove between the barrier ribs. Hence, bore diameter D isusually determined to 30 to 130 μm. Header 230 is structured so as tohave a linear movement by a header scanning mechanism (not shown).Continuously ejecting phosphor ink 250 from nozzle 240 while scanningheader 230 allows phosphor ink to be uniformly applied into the groovesbetween barrier ribs 109 on rear glass substrate 102. Viscosity ofphosphor ink 250 is kept within the range of 1500 to 50000 centipoises(CP) at a temperature of 25° C. This server 210 also has a mixer (notshown). Mixing prevents precipitation of particles in phosphor ink 250.Header 230 is integrally formed with ink chamber 230 a and nozzle 240 byperforming machining and electric discharge machining on a metallicmaterial.

Next will be described how to prepare phosphor ink 250. The phosphor inkis prepared by mixing phosphor particles of each color, a binder, and asolvent so that the mixture has a viscosity ranging 1500 to 50000centipoises (CP). A surface-active agent and a dispersant in an amountof 0.1 to 5 wt % can also be added, as required. Each phosphor particletypically used for the phosphor ink above is: BaAl₁₂O₁₉:Mn²⁺,Zn₂SiO₄:Mn²⁺, (Y, Gd)BO₃:Tb³⁺ for the green phosphor;Ba_(1-x)MgAl₁₀O₁₇:Eu²⁺ _(x), Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu²⁺ _(x) for theblue phosphor; and (Y, Gd)BO₃:Eu³⁺, Y₂O₃:Eu³⁺ for the red phosphor. Theamount of charge of each phosphor above is controlled ranging from −0.01μC/g to +0.01 μC/g, which will be explained later in the first and thesecond embodiments.

As for a binder included in phosphor ink 250, ethyl cellulose or acrylicresin can be used in an amount of 0.1 to 10 wt % of the ink. α-terpineolor n-butylcarbitol can be used as a solvent. Polymers, such as PMA andPVA, can also be used as a binder. As for a solvent, organic solvent,such as diethyleneglycol and methyl ether, can also be used.

Now turning back to manufacturing PDP 100. The front panel and the rearpanel described earlier are attached with each other so that the displayelectrode pairs on the front panel are located orthogonal to the addresselectrodes on the rear panel. Sealing glass is inserted between thepanels along the periphery thereof and baked, for example, attemperatures of approx. 450° C. for 10 to 20 min. to form hermeticalseal layer 121 (shown in FIG. 1) for sealing. Next, discharge space 122is once evacuated to a high vacuum (e.g. 1.1×10⁻⁴ Pa) and filled with adischarge gas, namely, He—Xe or Ne—Xe inert gas at a predeterminedpressure. Through the process above, PDP 100 is completed. Suchmanufactured PDP experiences 5-hour aging process with application ofdischarge voltage of 185 V and 200 kHz.

Hereinafter will be described how to control the amount of charge of thephosphor of the present invention.

FIRST EXEMPLARY EMBODIMENT

First, the description will be given on preparingBaAl₁₂O₁₉:Mn²⁺[xBaO.yAl₂O₃.zMnO.bMO] as a green phosphor so as to have apositive charge amount of +0.95 μC/g when the phosphor consists of mainmaterials; where, MO represents a compound to control the amount ofcharge of the phosphor to be prepared. The aforementioned green phosphorcontains barium carbonate (BaCO₃), manganese carbonate (MnCO₃), aluminumoxide (Al₂O₃) as the main materials, and compound MO that contains anelement bearing electronegativity of at least 1.5 so that the phosphorto be prepared can maintain the amount of charge close to zero. Oxidescan be contained in compound MO are as follows: titanium oxide (TiO₂,electronegativity: 1.6); tin oxide (SnO₂: 1.9); antimony oxide (Sb₂O₃:1.9); boron oxide (B₂O₃: 2.0); germanium oxide (GeO₂: 1.7); tantalumoxide (Ta₂O₅: 1.5); niobium oxide (Nb₂O₅: 1.6); vanadium oxide (V₂O₅:1.6); molybdenum oxide (MoO₃: 1.8); silicon oxide (SiO₂: 1.6).

Here will be described the preparation of a green phosphor by a solidphase synthesis method. First, mix barium carbonate (BaCO₃), magnesiumcarbonate (MgCO₃), aluminum oxide (Al₂O₃), manganese carbonate (MnCO₃)as a light-emitting substance, and compound MO in a molar ratio ofBaCO₃:MgCO₃:Al₂O₃:MnCO₃:MO=x:y:z:b (where, each range is preferably asfollows: 0.7≦x≦1.0, 5≦y≦6, 0.05≦z≦0.4, and 0.01≦b≦0.2). After that, adda small amount of flux (AlF₃) into the mixture. Next, bake the mixtureat 1100-1500° C. for 2 hours in the air. After adding a light-crush tothe baked material to remove lumps from the materials, bake it at1200-1500° C. in a N₂, or N₂—H₂ atmosphere. The green phosphor having anamount of charge close to zero is thus obtained.

To produce the phosphor having an amount of charge close to zero, themixing ratio of the material (i.e., x:y:z:b) has to be properlydetermined; however, as for amount b of compound MO, actual preparationtells that the phosphor with amount of charge close to zero can beobtained as long as 0.01≦b≦0.2. The fact is explained by an action, inwhich adding compound MO adjusts the amount of charge of a phosphorparticle close to zero, accordingly, minimizing the discharge energy ofthe particle. That is, useless material is naturally eliminated throughthe preparation process.

Next will be described the preparation of the green phosphor by ahydrothermal synthesis method. In a mixed solution fabrication process,materials of the phosphor, i.e., barium nitrate [Ba(NO₃)₂], aluminumnitrate [Al(NO₃)₃.9H₂O], manganese nitrate [Mn(NO₃)₂], and nitrate[M(NO₃)_(n)] that is an oxide for controlling amount of charge are mixedin a molar ratio of x:y:z:b. This mixture is dissolved in an aqueousmedium to prepare a mixed solution. Next, add a basic solution, such asammonia solution, to the hydrate mixed solution prepared above toproduce a hydrate. After that, put the hydrate and ion-exchanged waterinto a capsule made of a corrosion- and heat-resistant material, such asplatinum and gold. Then, the capsuled material undergoes hydro-thermalsynthesis in a high pressure vessel, using, for example, an autoclave,for 2-20 hours at 100-300° C. with application of pressure of 0.2-10MPa. Next, the obtained precursor powder is baked at 1200-1500° C. in aN₂, or N₂—H₂ atmosphere. The green phosphor having an amount of chargeclose to zero is thus obtained. The amount of charge of the phosphor canbe changed by controlling each amount of x, y, z, and b.

Next, the description will be given on preparing (Y, Gd)BO₃:Tb³⁺[(1-x-y)Y₂O₃.xGd₂O₃.B₂O₃.yTb.₂O₃.bMO], which is a green phosphor bearingpositive (+) charge when the phosphor consists of main materials. Eachrange of x, y, and b is preferably determined as follows: 0≦x≦0.5,0.05≦y≦0.3, and 0.01≦b≦0.1. The main materials of the chemical formulaabove—yttrium oxide (Y₂O₃), gadolinium oxide (Gd₂O₃), boron oxide(B₂O₃), and terbium oxide (Tb₂O₃)—encourage the phosphor to bearpositive (+) charge. Therefore, in order to control the amount of chargeof the phosphor close to zero, an oxide that tends to bear negative (−)charge due to its great electronegativity should be mixed, with a propermolar ratio, with the main materials. In this case, titanium oxide(TiO₂), tin oxide (SnO₂), antimony oxide (Sb₂O₃), boron oxide (B₂O₃),germanium oxide (GeO₂), tantalum oxide (Ta₂O₅), niobium oxide (Nb₂O₅),vanadium oxide (V₂O₅), molybdenum oxide (MoO₃), and silicon oxide (SiO₂)are the preferable compounds. After that, bake the mixture with a smallamount of flux, such as NH₄Cl, at from 1000° C. to 1400° C. in a N₂, orN₂—H₂ atmosphere. Through the process, the green phosphor having anamount of charge close to zero is obtained.

Next, the description will be given on preparing Ba_(1-x)Mg₁₀O₁₇:Eu_(x)²⁺[(1-x)BaO.x/2Eu₂O₃.MgO.5Al₂O₃.bMO], which is a blue phosphor bearingpositive (+) charge when the phosphor consists of main materials. Themain materials above—barium carbonate (BaCO₃), europium oxide (Eu₂O₃),magnesium carbonate (MgCO₃), aluminum oxide (Al₂O₃), and compound MO forcontrolling the amount of charge of the phosphor are mixed in a molarratio of 1-x:x/2:1:5:b (where, 0.03≦x≦0.3, 0.01≦b≦0.2). As the oxide ofcompound MO, at least one is selected from the followings: titaniumoxide (TiO₂), tin oxide (SnO₂), antimony oxide (Sb₂O₃), boron oxide(B₂O₃), germanium oxide (GeO₂), tantalum oxide (Ta₂O₅), niobium oxide(Nb₂O₅), vanadium oxide (V₂O₅), molybdenum oxide (MoO₃). The mixedpowder is baked at, for example, 1350° C. for two hours in a reducingatmosphere containing 5% of hydrogen and 95% of nitrogen, and then thepowder is classified. Through the process, with the help of the oxidecontrolling the amount of charge, Ba_(1-x)MgAl₁₀O₁₇:Eu²⁺ _(x), the bluephosphor having an amount of charge close to zero is thus obtained.

The amount of charge of the phosphor is measured by the blow-off chargemeasurement. Properly determining the values of x and b contributes tothe amount of charge close to zero.

The blue phosphor of Ba_(1-x-y)SryMgAl₁₀O₁₇:Eu_(x), in which Ba ispartially replaced with Sr (where, 0.1≦y≦0.5), is prepared by the solidreaction method. Like the blue phosphor of Ba_(1-x)MgAl₁₀O₁₇;Eu_(x), theblue phosphor of Ba_(1-x-y)SryMgAl₁₀O₁₇:Eu_(x) is also controlled theamount of charge through the same preparation method.

Next will be described a typical method of oxide coating. In the method,a blue phosphor bearing positive (+) charge that consists of mainmaterials is coated with an oxide bearing negative (−) charge, so thatthe amount of charge approximates to zero. Ba_(1-x)MgAl₁₀O₁₇;Eu_(x) orBa_(1-x-y)SryMgAl₁₀O₁₇:Eu_(x) can be used as a blue phosphor in themethod.

To achieve a high luminance, the values of x and y should preferablytake the ranges: 0.03≦x≦0.3, 0.1≦y≦0.5. The amount of positive (+)charge of the aforementioned blue phosphors ranges from +0.5 μC/g to+1.3 μC/g. For example, negative charge carrying oxides includestitanium oxide (TiO₂), tin oxide (SnO₂), antimony oxide (Sb₂O₃),germanium oxide (GeO₂), tantalum oxide (Ta₂O₅), niobium oxide (Nb₂O₅),vanadium oxide (V₂O₅), molybdenum oxide (MoO₃), and silicon oxide(SiO₂). As coating material suitable for the phosphor, colloidalsolution containing the aforementioned oxides, or water-soluble saltcontaining metallic element M—among others, β-diketone [M(C₅H₇O₂)_(n)],and alkoxy organometal [M(OR)_(n)], where R represents alkyl group—ispreferably used. As the first step of the preparation, mix the mainmaterial of the blue phosphor with the coating material containing anoxide above in aqueous solution containing alcohol. Dry the mixture andbake it at 600-1000° C. The surface of the phosphor is coated with theoxide through a chemical bond, whereby the amount of charge of thephosphor is kept close to zero. The amount of charge of the phosphor canbe controlled by varying the coating amount of the oxide and the bakingtemperature.

Next, the description will be given on preparing (Y, Gd)BO₃:Eu³⁺[x(Y,Gd)₂O₃.B₂O₃.yEu₂O₃.bMO], which is a red phosphor bearing positive (+)charge when the phosphor consists of main materials. First, mix the mainmaterials above—yttrium oxide (Y₂O₃), gadolinium oxide (Gd₂O₃), boronoxide (B₂O₃), and europium oxide (Eu₂O₃)—with compound MO forcontrolling the amount of charge of the phosphor are mixed in a molarratio of x:y:1:b (where, Y:Gd=65:35). Next, bake the mixture at1200-1350° C. for 2 hours in the air. After baking, classify thematerial to obtain the red phosphor. Each value of x, y and b should bedetermined so that the amount of charge gets close to zero.

Another red phosphor of Y₂O₃:Eu³⁺[xY₂O₃.yEu₂O₃.bMO], which bearspositive (+) charge when the phosphor consists of main materials, isprepared as is the case of the aforementioned phosphor of (Y, Gd)BO₃:Eu.Each value of x, y and b should be also determined so that the amount ofcharge gets close to zero.

SECOND EXEMPLARY EMBODIMENT

Here in the embodiment will be described how to control the amount ofcharge, taking preparation of a green phosphor ofZn₂SiO₄:Mn²⁺[2(1-x)ZnO.2xMnO.ySiO₂.bMO]. The aforementioned greenphosphor bears negative (−) charge of approx. −1.5 μC/g when thephosphor is formed of main materials alone. Therefore, to approximatethe amount of charge of the phosphor to zero, a sub material havingsmall electronegativity is added to the main materials. For example,zinc oxide (ZnO), yttrium oxide (Y₂O₃), aluminum oxide (Al₂O₃), bismuthoxide (Bi₂O₃), and magnesium oxide (MgO) can be the compounds to beadded. In the preparation, mix the aforementioned compound with the mainmaterials according to a molar ratio determined so as to approximate theamount of charge to zero, and then bake the mixture at 1000-1400° C. ina N₂, or N₂—H₂ atmosphere. The green phosphor having an amount of chargeclose to zero is thus prepared. Prior to the preparation, each value ofx, y and b should be optimized so that the amount of charge gets closeto zero. Although adding such a metallic element to the phosphormaterial is greatly effective in controlling the amount of charge, therehas been a worry in which the metallic elements would unfavorably workas an activator for unintended emitting, or work as a killer center thatinvites poor luminance. However, selecting proper combination ofmaterials can provide an excellent phosphor having an amount of chargeclose to zero without ill effect.

The descriptions have so far given on a method of controlling the amountof charge in which a compound bearing charges opposite to that of themain materials is added or used as a coating material, that is, anegatively (−) charged compound is used for a positively (+) chargedphosphor when the phosphor consists of the main materials, and viceversa.

Other than the method above, the amount of charge of a phosphor can becontrolled by adding a compound having an amount of charge of nearlyzero, as an additive or a coating material, to phosphor material bearingpositive (+)/negative (−) charge when the phosphor consists of mainmaterials. To be more specific, applying an oxide having an amount ofcharge almost zero, such as manganese oxide (MnO₂), chrome oxide(Cr₂O₃), boron oxide (B₂O₃), and zirconium oxide (ZrO₂), to the surfaceof a phosphor particle to form an extremely thin coat (few nanometers)thereover. Through the coating, the amount of charge of the phosphor canbe settled close to zero.

Here will be describe an example in which the surface of a phosphorparticle of Zn₂SiO₄:Mn²⁺ is coated with boron oxide (B₂O₃). The phosphorformed of Zn₂SiO₄:Mn²⁺ bears negative charge of −1.5 μC/g when thephosphor consists of main materials alone, whereas the amount of chargeof the coating material of B₂O₃ is substantially zero; correctly, usedas an additive, the oxide of B₂O₃ tends to bear negative (−) charge dueto the electronegativity of the B element, on the other hand, used as acoating material, the molecule of B₂O₃ has no noticeable characteristicsin amount of charge.

In the preparation process, firstly, hydrolyze the phosphor material ofZn₂SiO₄:Mn²⁺ and a boron-containing alkoxide compound, such asB(OC₂H₅)₃, or organometallic compound, such as B(C₅H₇O₂)₃, in analcoholic solution. Through the hydrolysis, the surface of a phosphorparticle is uniformly coated with B₂O₃ in a thickness of 5-20 nm. As thenext step, bake the phosphor particles at 500-900° C. in the air. Inthis way, the amount of charge of the phosphor can be approximated tozero. According to differences in amount of charge of phosphors to beprepared, the thickness of the coating material (B₂O₃) and/or the bakingtemperature can be increased or decreased to obtain an amount of chargeclose to zero.

It will be understood that the control method of amount of charge byemploying a compound having an amount of charge of substantially zero asa coating material is also applicable to other phosphor materials.

EXPERIMENT

In order to evaluate the performance of a plasma display unit of thepresent invention, samples based on the first and second embodimentswere prepared to carry out performance evaluation tests. Each of theplasma display units produced as samples has a diagonal size of 42 in.for a high definition (HD) TV screen having a rib-pitch of 150 μm. Eachof the PDP was produced so that the dielectric glass layer was 20 μmthick; the MgO protective layer was 0.5 μm thick; and the distancebetween each display electrode and each display scan electrode was 0.08mm. The discharge space was filled with a discharge gas in which 5% ofxenon gas was mixed with neon as the major component. The discharge gaswas sealed in the discharge space with the application of specifieddischarging gas pressure of, for example, 66.5 kPa.

Table 1 shows the composition of each phosphor sample used forevaluation of a plasma display unit and compounds for controlling amountof charge mixed into the phosphor samples. TABLE 1 Green phosphor Bluephosphor xBaO.yAl₂O₃.zMnO.bMO [(1 − x)BaO.xEuO.MgO.5Al₂O₃.bMO] Redphosphor MO MO [x(Y,Gd)₂O₃.yEu₂O₃.B₂O₃.bMO] (material (material MO Sam-and and (material and ple Amount Amount Amount Amount applying Amount ofAmount applying applying No. of BaOx of y of z of b method) Eu x of bmethod) x Y b method) 1 1 5.00 0.3 0.1 Sb₂O₅ 0.10 0.1 B₂O₃ 0.8 0.2 0.1MoO₃ added added added 2 0.75 6.00 0.2 0.05 B₂O₃ x = 0.2 0.05 Nb₂O₅ 0.90.1 0.05 GeO₂ coating coating coating 3 0.8 5.50 0.4 0.01 TiO₂ x = 0.30.01 Ta₂O₃ 0.85 0.15 0.01 ZrO₂ added coating coating 4 0.9 6.00 0.250.03 V₂O₅ x = 0.15 0.03 SnO₂ 0.75 0.25 0.03 SiO₂ added coating coatingBlue phosphor [(1 − x)(Ba,Sr)O.xEuO.MgO.5Al₂O₃.bMO] Red phosphor Greenphosphor MO [xY₂O₃.yEu₂O₃.B₂O₃.bMO] 2(1 − x)ZnO.2xMnO.ySiO₂.bMO(material MO Sam- MO and (material and ple Amount Amount Amount(material and Amount of Amount applying applying No. of x of y of bapplying method) Eu x of b method) x Y b method) 5 0.1 0.90 0.05 Al₂O₃0.10 0.1 Sb₂O₃ 0.9 0.1 0.03 ZrO₂ coating added coating 6 0.15 0.80 0.1ZnO 0.20 0.05 Nb₂O₅ 0.85 0.15 0.01 GeO₂ added coating coating 7 0.2 0.700.01 Y₂O₃ 0.15 0.01 SnO₂ 0.8 0.2 0.1 B₂O₃ coating coating added 8 0.250.60 0.02 Bi₂O₃ 0.20 0.03 MoO₂ 0.75 0.25 0.05 Nb₂O₃ coating addedcoating 9 0.15 0.80 0.05 MgO 0.15 0.02 SiO₂ 0.70 0.30 0.06 SnO₄ addedcoating coating Green phosphor mixture of xBaO.yAl₂O₃.zMnO.bMO andx(Y,Gd)₂O₃.yTb₂O₃.B₂O₃.bMO Blue phosphor (mixing ratio 45:55) (1 −x)BaO.xEuO.MgO.5Al₂O₃.bMO Red phosphor MO MO xY₂O₃.yE₂O₃.bMO (material(material MO Sam- and and (material and ple Amount Amount Amount Amountapplying Amount of Amount applying applying No. of x of y of z of bmethod) Eu x of b method) x Y b method) 10  BaOx = Al₂O₃ y = MnOz = 0.02GeO₂ 0.1 0.02 GeO₂ 0.9 0.1 0.03 Sb₂O₃ 1.0 6 0.25 coating added added(Y,Gd)x = Tb2O3y = 0.9 0.1 11  BaOx = Al₂O₃ y = MnOz = 0.03 B₂O₃ 0.10.03 B₂O₃ 0.85 0.15 0.04 B₂O₃ 0.9 6 0.25 coating coating added (Y,Gd)x =Tb2O3y = 0.8 0.2 12  BaOx = Al₂O₃ y = MnOz = 0.04 Nb₂O₃ 0.1 0.04 Nb₂O₃0.75 0.2 0.05 Nb₂O₃ 0.8 5.5 0.3 coating coating added (Y,Gd)x = Tb₂O₃ y= 0.7 0.3 13* Green phosphor Blue phosphor Red phosphor1.8Zn.0.2MnO.SiO₂ 0.9BaO.MgO.0.1EuO.5Al₂O₃ 0.8(Y,Gd)₂O₃.B₂O₃.0.2Eu₂O₃ (x= 0.1, b = 0) (x = 0.1, b = 0) (x = 0.8, y = 0.2, b = 0 14* Greenphosphor Blue phosphor Red phosphor mixture of0.8(Y,Gd)₂O₃.0.2Tb₂O₃.B₂O₃ and 0.9BaO.MgO.0.1EuO.5Al₂O₃0.8(Y,Gd)₂O₃.B₂O₃.0.2Eu₂O₃ 1.8Zn.0.2MnO.SiO₄ (mixinig ratio 50:50) (x =0.1, b = 0) (x = 0.8, y = 0.2, b = 0 amount of charge: 0.015 μC/g 15*Green phosphor mixture of the blue phosphor of sample mixture of the redphosphor of sample mixture of 0.8(Y,Gd)₂O₃.0.2Tb₂O₃.B₂O₃ and 13* andNb₂O₃ 13* and SiO₂ 1.8Zn.0.2MnO.SiO₄ (mixinig ratio 50:50) (amount ofNb₂O₃: 2%) (amount of SiO₂: 1.5%) amount of charge: 0.015 μC/g*Samples 13* through 15* are comparative examples.

Samples 1 through 4 are structured so as to have a combination of thegreen phosphor of [xBaO.yAl₂O₃.zMnO.bMO], the blue phosphor of[(1-x)BaO.x/2Eu₂O₃. MgO.5Al₂O₃.bMO], and the red phosphor of [x(Y,Gd)₂O₃.yEu₂O₃.B₂O₃.bMO (where, Y:Gd=65:35)]. The amount of charge of allthe phosphors of the aforementioned samples, as shown in Table 2,achieves within ±0.01 μC/g.

Samples 5 through 9 are structured so as to have a combination of thegreen phosphor of [2(1-x)ZnO.2xMnO.ySiO₂.bMO], the blue phosphor of[(1-x)(Ba, Sr)O.x/2Eu₂O₃.MgO.5Al₂O₃.bMO (where, Ba:Sr=80:20)], and thered phosphor of [xY₂O₃yEu₂O₃.B₂O₃.bMO]. The amount of charge of all thephosphors of the aforementioned samples, as shown in Table 2, achieveswithin ±0.01 μC/g.

Samples 10 through 12 are structured so as to have a combination of twokinds of green phosphors of [xBaO.yAl₂O₃.zMnO.bMO] and [x(Y,Gd)₂O₃.B₂O₃.yTb₂O₃.bMO (where, Y:Gd=50:50)] in a mixing ratio of[xBaO.yAl₂O₃.zMnO.bMO]: [x(Y, Gd)₂O₃.B₂O₃.yTb₂O₃.bMO]=45:55, the bluephosphor of [(1-x)BaO.x/2Eu₂O₃.MgO.5Al₂O₃.bMO], and the red phosphor of[xY₂O₃.yEu₂O₃.bMO]. The amount of charge of all the phosphors of theaforementioned samples, as shown in Table 2, achieves within ±0.01 μC/g.

Samples 13*, 14*, and 15* are prepared as comparative samples. Thecomparative samples are formed of combination of conventional phosphorsof three colors, each of which consists of main materials, that is, eachof which is given no improvement in amount of charge. Sample 13* hasfollowing combination: a conventional green phosphor of[1,8ZnO.0.2MnO.SiO₂ (where, x=0.1, y=1, b=0)] having an amount of chargeof −1.5 μC/g; a conventional blue phosphor of [0.9BaO.MgO.0.1EuO.5Al₂O₃(x=0.1, b=0)] having an amount of charge of +1.2 μC/g; and aconventional red phosphor of [0.8(Y, Gd)₂O₃.B₂O₃.0.2Eu₂O₃.bMO (x=0.8,y=0.21, b=0, and Y:Gd=65; 35)] having an amount of charge of +1.1 μC/g.

The green phosphor employed for sample 14* consists of 50% of [0.8(Y,Gd)₂O₃.B₂O₃.0.2Tb₂O₃ (where, Y:Gd=50:50)] having an amount of charge of+1.4 μC/g; and 50% of [Zn₂SiO₄:Mn²⁺] having an amount of charge of −1.5μC/g, so that the apparent amount of charge of +0.015 μC/g is obtained.As for the blue phosphor and the red phosphor, [Ba1-xMgAl₁₀O₁₇:Eu_(x)²⁺] having an amount of charge of +1.3 μC/g and [(Y, Gd)BO₃:Eu³⁺] havingan amount of charge of +1.1 μC/g are used, respectively.

The green phosphor of sample 15* has the same composition as that ofsample 14*. As for the blue phosphor and the red phosphor, an oxide isadded to each phosphor employed for sample 14*; the blue phosphor isprepared in such a way that Nb₂O₃ bearing negative (−) charge is mixed(where, the mixing ratio of Nb₂O₃ is 3%) into the blue phosphor of[0.9BaO.MgO.0.1EuO.5Al₂O₃ (x=0.1, b=0)] with an amount of charge of +1.2μC/g, so that the apparent amount of charge is controlled to +0.002μC/g. Similarly, the red phosphor is prepared in such a way thatcompound SiO₂ bearing negative (−) charge is mixed (where, the mixingratio of SiO₂ is 1.5%) into the red phosphor of [(Y, Gd)BO₃:Eu³⁺] withan amount of charge of +1.1 μC/g, so that the apparent amount of chargeis controlled to −0.003 μC/g.

Evaluation Experiment 1

The inventors examined the amount of charge of each phosphor of samples1 through 12, and comparative samples 13*, 14*, and 15* with a blow-offcharge measuring device. The result tells that the amount of charge ofall the phosphors employed for samples 1 through 12 are settled within±0.01 μC/g.

Evaluation Experiment 2

The luminance degradation of each phosphor and of the panel displayingwhite was tested as follows. Discharge sustain pulses at a voltage of185V and at a frequency of 200 kHz were applied to each sample PDPcontinuously for 1000 hours, and luminance of each PDP was measuredbefore and after the application of the pulses. Based on themeasurements, the luminance degradation factor was derived from theexpression of ((luminance after pulse-application−luminance beforepulse-application)/luminance before pulse-application)*100. Addressingfailure at address discharge was determined by existence of flickers inan image. If a sample PDP has flickers in any one position, the PDP wasjudged as having flickers.

Evaluation Experiment 3

Green phosphor ink was applied through a nozzle with a diameter of 100μm continuously for 100 hours. After that, evaluations were given on theabsence or presence of a clogged nozzle, of inconsistencies in phosphorcoat (after dried), and of improper alignment of color while responsibledischarge cells are turning ON.

The results obtained from the evaluation experiments 1 through 3 theluminance degradation of the each panel displaying white, the luminancedegradation of each phosphor, the absence or presence of inconsistenciesin coating; improper alignment of color; addressing failure at addressdischarge; a clogged nozzle—are listed in Table 2. TABLE 2 Luminancedegradation factor (%) of panel after the application of dischargesustain Luminance pulses degradation factor Inconsistencies (185 V, (%)of each phosphor in coating of Addressing 200 kHz) for after theapplication panel failure at Amount of charge of 1000 hrs. of dischargesustain and address phosphor at pulses (185 V, improper discharge Sample(μC/g) displaying 200 kHz) for 1000 hrs. alignment of and No. Green BlueRed all white Green Blue Red color clogged nozzle 1 −0.005 −0.006 −0.008−2.4 −2.1 −0.6 0.1 None Both none 2 −0.009 0.001 0.003 −2.5 −2.3 −0.50.2 None Both none 3 0.007 0.009 0.01 −2.5 −2.1 −0.7 −0.2 None Both none4 0 −0.005 0.006 −1.7 −1.0 −0.6 0.4 None Both none 5 −0.01 −0.007 0.008−2.9 −2.5 −0.8 0.5 None Both none 6 0.008 0.002 0.01 −2.7 −2.3 −1.0 −0.3None Both none 7 −0.008 0.003 0 −2.5 −2.1 −0.7 0.1 None Both none 8 0.010.001 0.006 −2.8 −2.7 −0.5 −0.3 None Both none 9 −0.009 −0.002 0.002−2.7 −2.4 −0.6 0.2 None Both none 10  0.006 0.01 0.009 −2.7 −2.3 −0.9−1.0 None Both none 11  0 0.007 0.001 −1.5 −1 −0.6 0.3 None Both none12  0.002 0.005 0.005 −2.2 −1.9 −0.6 0.4 None Both none 13* −1.5 1.2 1.1−15.8 −14.8 −3.5 −3.5 Observed Both observed 14* 0.015 1.3 1.1 −13.6−12.5 −3 −4 Observed Both observed 15* 0.015 0.002 −0.003 −15.8 −14.3−1.0 0.2 No No clogged inconsistency in nozzle, but coating addressingfailure was observed*Samples 13*, 14*, and 15* are comparative samples.

Comparative samples 13*, 14*, and 15* are formed of combination ofconventionally employed phosphors. As shown in Table 2, the amount ofcharge of each comparative sample is more than 100 times the amount ofcharge of the phosphor of samples 1 through 12. Because of such a largeamount of charge, application of the phosphor ink easily invitesinconsistencies in color or improper color mixing due to inconsistenciesin coating by friction caused when the ink passes through a narrownozzle. Besides, the phosphor easily absorbs water or hydrocarbon-basedgas. This fact considerably degrades the luminance of each phosphor,thereby producing misalignment of color, accordingly, the luminance whenthe panel displays white is significantly impaired.

On the other hand, the phosphors of samples 1 through 12 have an amountof charge close to zero. Therefore, the luminance in discharging isproperly maintained. Besides, none of addressing failure at addressdischarge, a clogged nozzle, and misalignment of color was observed.

Comparative sample 14* employs the phosphor of Zn₂SiO₄:Mn²⁺ bearingnoticeable negative (−) charge and the phosphor of (Y, Gd)BO₃:Tb³⁺bearing noticeable positive (+) charge to form the green phosphor. Thetwo kinds of phosphors are simply mixed with each other to obtain thegreen phosphor having apparent amount of charge of 0.015 μC/g. Althoughthe apparent amount of charge is close to zero, each phosphor particleforming the green phosphor have large amount of charge, thereby theparticles easily capture water, carbon monoxide (CO), carbon dioxide(CO₂), or hydrocarbon-based gases. This fact means increase in undesiredgas emission when the panel is in operation, so that 147 nm-ultravioletlays and discharge sustain pulses contribute to luminance degradation.Furthermore, addressing failure and a clogged nozzle easily occur.

In comparative sample 15*, each of the three phosphors has an amount ofcharge as low as those of samples 1 through 12; there is little worryabout inconsistency in coating or a clogged nozzle. However, suppressingthe amount of charge relatively low by simple mixing (i.e., withoutchemical bonding) cannot expect to decrease the gas absorption by thephosphor particles, thereby exhibiting luminance degradation bydischarging.

In contrast, in the PDPs employing the combination of the green, blue,and red phosphors of samples 1 through 12, the oxides added or coated toeach phosphor experience a baking process at high temperatures, so thatthe oxide and the phosphor are chemically bonded. The amount of chargeof the surface of a phosphor particle is therefore kept close to zero,whereby impurity gases are hard to be captured by the phosphor.Accordingly, luminance degradation of each color by 147 nm-Ultravioletrays or discharge sustain pulses, and changes in temperature of thecolor are minimized. These advantages contribute to an improvedluminance when a panel displays white. Besides, neither addressingfailure nor a clogged nozzle in applying phosphors occurs.

INDUSTRIAL APPLICABILITY

According to the present invention, a phosphor conventionally used for aplasma display unit, which bears positive or negative charge, is coatedwith a compound for controlling the amount of charge of the phosphorthrough a strong chemical bonding, whereby the amount of charge of aphosphor can be suppressed within ±0.01 μC/g. Controlling the amount ofcharge of phosphors close to zero can keep impurity gases away from thephosphor particle when the panel is in operation, suppressing problemscritical to driving a plasma display unit, such as luminance degradationof phosphors, improper color alignment of images in panel operation,luminance degradation when the panel displays all white, andinconsistencies in applying phosphors. A high quality plasma displayunit can be thus obtained.

1. A plasma display unit at least containing a front panel and a rearpanel in a confronting arrangement via discharge space, the front panelhaving a plurality of display electrode pairs disposed on a glasssubstrate, and the rear panel having a plurality of address electrodesthat forms discharge cells in combination with the display electrodepairs, and a phosphor layer for emitting by discharging, wherein in thecase that a surface of the phosphor layer bears positive (+) charge whenthe phosphor layer is formed of main material alone, an oxide containingan element with electronegativity larger than an oxide included in themain material is added or used as a coating material in order tosuppress an amount of charge of the phosphor layer within ±0.01 μC/g. 2.The plasma display unit of claim 1, wherein the main material is formedof an aluminate-based green phosphor of BaAl12O19:Mn2+.
 3. The plasmadisplay unit of claim 1, wherein the main material is formed of ayttrium oxide-based green phosphor of (Y, Gd)BO3:Tb3+.
 4. The plasmadisplay unit of claim 1, wherein the main material is formed of analuminate-based blue phosphor of Ba1-xMgAl10O17:Eux2+ orBa1-x-ySryMgAl10O17:Eux2+.
 5. The plasma display unit of claim 1,wherein the main material is formed of a yttrium oxide-based redphosphor of (Y, Gd)BO3:Eu3+ or Y2O3:Eu3+.
 6. The plasma display unit ofclaim 1, wherein the oxide is at least any one of titanium oxide (TiO2);tin oxide (SnO2); germanium oxide (GeO2); tantalum oxide (Ta2O5);niobium oxide (Nb2O5); vanadium oxide (V2O5); molybdenum oxide (MoO3);boron oxide (B2O3); silicon oxide (SiO2); and antimony oxide (Sb2O3). 7.A plasma display unit at least containing a front panel and a rear panelin a confronting arrangement via discharge space, the front panel havinga plurality of display electrode pairs disposed on a glass substrate,and the rear panel having a plurality of address electrodes that formsdischarge cells in combination with the display electrode pairs, and aphosphor layer for emitting by discharging, wherein in the case that asurface of the phosphor layer bears negative (−) charge when thephosphor layer is formed of main material alone, an oxide containing anelement with electronegativity smaller than an oxide included in themain material is added or used as a coating material in order tosuppress an amount of charge of the phosphor layer within ±0.01 μC/g. 8.The plasma display unit of claim 7, wherein the main material is formedof a silicate-based green phosphor of Zn2SiO4:Mn2+.
 9. The plasmadisplay unit of claim 7, wherein the oxide is at least any one of zincoxide (ZnO); yttrium oxide (Y2O3); aluminum oxide (Al2O3); bismuth oxide(Bi2O3); magnesium oxide (MgO).
 10. A phosphor having an amount ofcharge suppressed within ±0.01 μC/g obtained by adding an oxide as a submaterial containing an element with electronegativity larger than anoxide of main material into the main material, or by applying the oxideas a coating material on a surface of a phosphor layer, in the case thatthe surface of the phosphor layer bears positive (+) charge when thephosphor layer is formed of main material alone.
 11. The phosphor ofclaim 10, wherein the main material is formed of an aluminate-basedgreen phosphor of BaAl12O19:Mn2+.
 12. The phosphor of claim 10, whereinthe main material is formed of a yttrium oxide-based green phosphor of(Y, Gd)BO3:Tb3+.
 13. The phosphor of claim 10, wherein the main materialis formed of an aluminate-based blue phosphor of Ba1-xMgAl10O17:Eux2+ orBa1-x-ySryMgAl10O17:Eux2+.
 14. The phosphor of claim 10, wherein themain material is formed of a yttrium oxide-based red phosphor of (Y,Gd)BO3:Eu3+ or Y2O3:Eu3+.
 15. The phosphor of claim 10, wherein theoxide is at least any one of titanium oxide (TiO2); tin oxide (SnO2);germanium oxide (GeO2); tantalum oxide (Ta2O5); niobium oxide (Nb2O5);vanadium oxide (V2O5); molybdenum oxide (MoO3); boron oxide (B2O3);silicon oxide (SiO2); and antimony oxide (Sb2O3).
 16. A phosphor havingan amount of charge suppressed within ±0.01 μC/g obtained by adding anoxide as a sub material containing an element with electronegativitysmaller than an oxide of main material into the main material, or byapplying the oxide as a coating material on a surface of a phosphorlayer, in the case that the surface of the phosphor layer bears negative(−) charge when the phosphor layer is formed of main material alone. 17.The phosphor of claim 16, wherein the main material is formed of asilicate-based green phosphor of Zn2SiO4:Mn2+.
 18. The phosphor of claim16, wherein the oxide is at least any one of zinc oxide (ZnO); yttriumoxide (Y2O3); aluminum oxide (Al2O3); bismuth oxide (Bi2O3); magnesiumoxide (MgO).